THE HISTOET OE EXPLOSIVE AGENTS. 
513 
In considering the manner in which a detonation operates in determining the violent 
explosion of gun-cotton and nitroglycerine in open air, I have, for the sake of simplicity, 
confined myself to an examination of the manner in which those particular explosive 
substances are affected by the disturbing agency in question. It must not, however, be 
supposed that the power to exert a violent explosive action, when unconfined or partly 
exposed to air, is limited to explosive compounds. A few experiments instituted with 
explosive mixtures (produced by the intimate incorporation of powerful oxidizing agents 
and readily oxidizable substances, the combustion of which furnishes gases or vapours) 
have demonstrated that the destructive or explosive force of these may also be fully 
developed under conditions most unfavourable to their operation as explosive agents, 
under ordinary circumstances, if they are submitted to the influence of a detonation. 
Mixtures of potassic chlorate with the sulphides of antimony or arsenic, with potassic 
ferro- or ferri-cyanide, with potassic picrate, and other explosive mixtures of similar 
nature, and lastly even gunpowder, have been readily made to explode, when unconfined, 
with the full force which they are capable of exerting, by being placed in contact with 
a confined charge of mercuric fulminate. As far as could be determined by small com- 
parative experiments, the readiness with which the violent explosion of these mixtures 
can be developed is, as might be anticipated, in direct proportion to their sensitiveness 
to explosion by percussion. Thus a mixture of the potassic picrate and chlorate, freely 
exposed to air, is exploded apparently with as much facility as gun-cotton by the deto- 
nation of a small fulminate-charge, and the violence of the explosion approaches that of 
gun-cotton fired under the same conditions. The detonation of a freely exposed mixture 
of the chlorate with sulphide of antimony is somewhat less readily accomplished, and 
the violent explosion of gunpowder requires the fulfilment of special conditions favour- 
able to the action of the detonating charge of fulminate. If the grains of a small charge 
of powder be merely heaped upon a flat surface, the case which contains the fulminate 
being inserted into the heap, they are simply scattered by the detonation of the fulmi- 
nate ; but if a corresponding quantity of gunpowder be so arranged that the dispersion 
of the grains is impeded (as by placing it in a cylinder quite open at the upper end), its 
violent explosion is accomplished with certainty. 
The following experiment affords an illustration of the difference in effect between 
the ignition of gunpowder in the ordinary manner, and by detonation, under precisely 
similar conditions. A small iron cylinder (4 inches long, 0T5 inch thick, and 1 inch 
internal diameter, closed at one end) was inserted into heavy clay soil so that its opening 
was on a level with the surface, and the earth was firmly rammed round it. The cylinder 
was then filled with fine-grain gunpowder, into the centre of which an ordinary electric 
fuse (primed with meal powder) was inserted. When the latter was ignited, the powder 
exploded with a dull report, and the force was entirely directed upwards, no effect being 
produced upon the cylinder or upon its position in the ground. A second precisely 
similar cylinder, enveloped by earth in the same way, was filled with sand, into which 
was inserted an electric fuse primed vrith mercuric fulminate. The explosion of the 
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